Process for the selective separation of fe, m and n in steel metallurgical dusts containing alkali metals m, volatile heavy metals n

Abstract

This invention belongs to the field of solid waste treatment, specifically relating to a method for the selective separation of Fe, M, and N from iron and steel metallurgical dust containing alkali metal M and volatile heavy metal N. The method involves mixing the iron and steel metallurgical dust with carbonaceous materials and pressing them into blocks. The blocks are then heated to temperature T1 using microwaves in a protective atmosphere, followed by a reduction treatment in a reducing atmosphere to obtain a tail gas enriched with volatile heavy metal N and a reduction slag enriched with elemental iron and alkali metal M. The reduction slag is then subjected to wet grinding and leaching to separate elemental iron and a solution enriched with alkali metal M. The alkali metal M includes at least one element selected from sodium and potassium; the volatile heavy metal N includes at least one element selected from lead and zinc. The temperature T1 is 800-900℃. The method provided by this invention can effectively suppress the accompanying volatilization of alkali metal M, preventing severe corrosion of the reaction equipment.

Description

Technical Field

[0001] This invention belongs to the field of solid waste resource utilization, and particularly relates to the treatment of iron and steel metallurgical dust. Background Technology

[0002] In the sintering, ironmaking, and steelmaking processes, large amounts of dust rich in iron, carbon, volatile heavy metals (such as zinc and lead), and alkali metals (such as potassium and sodium) are generated. Statistics show that metallurgical dust accounts for approximately 9% to 11% of steel production capacity, with zinc-containing dust accounting for 20% to 30%. If this dust is not efficiently and environmentally treated and utilized, it will not only result in a huge waste of strategic metal resources such as iron and zinc, but the abundant alkali metals (K and Na) and heavy metals (Pb and Zn) will also pose a serious threat to the environment, including soil and water, as well as biological health. Its high-value comprehensive utilization has become one of the key technological bottlenecks restricting the green and low-carbon development of the steel industry.

[0003] The composition of dust from iron and steel metallurgy is extremely complex, and its properties vary significantly depending on the production process. Blast furnace dust is typically rich in carbon and iron, while converter dust and electric furnace dust are rich in zinc, lead, and alkali metals. Valuable elements in these dusts often exist in complex associated mineral phases. For example, zinc often exists as zinc ferrite (ZnFe₂O₄), while alkali metals potassium and sodium mainly exist as their chlorides (KCl, NaCl). Lead may also appear as complex chloride salts (such as PbClF, Pb₂OFCl, etc.). This complex phase composition and elemental co-occurrence relationships are the fundamental reason why subsequent efficient separation and recovery are extremely difficult.

[0004] Currently, the primary method for steel companies to handle this type of dust is to return it to the sintering process for recycling. However, this approach has serious drawbacks. For example, the continuous accumulation of elements such as zinc, lead, potassium, and sodium in the dust can damage the strength of the sinter, reduce blast furnace permeability, corrode the blast furnace lining, and may cause blast furnace nodules, severely affecting the smooth operation and lifespan of the blast furnace. In particular, alkali metals, whose compounds are easily volatilized at high temperatures and condensed and accumulated in the equipment at low temperatures, have become a key obstacle restricting the comprehensive utilization of dust. Therefore, developing an external circulation treatment technology that can effectively separate and recover various valuable elements, and realize the "turning waste into treasure" of dust containing alkali metals such as potassium and sodium, as well as volatile heavy metals such as lead and zinc, is an urgent practical need and of great environmental protection significance.

[0005] Currently, the main methods for dust resource recovery and utilization include pyrometallurgical processes, hydrometallurgical processes, and combined pyrometallurgical and hydrometallurgical technologies. Among these, pyrometallurgical processes have been widely used and developed due to their advantages of simple processing and high consumption, and are currently the main means of dust treatment. Pyrometallurgical direct reduction processes, represented by the Waelz rotary kiln method and the rotary hearth furnace (RHF) method, are currently the most widely used dust treatment technologies. Their core is to reduce iron oxides in the dust to metallic iron through carbothermic reduction, while simultaneously allowing low-boiling-point zinc, lead, and other substances to volatilize and be enriched and recovered in the flue gas. Although this process is relatively mature, it has significant drawbacks. First, it relies on external high-temperature heating, with reaction temperatures typically exceeding 1100 °C, resulting in high energy consumption and significant carbon emissions. Second, traditional pyrometallurgical processes have limited removal capabilities for alkali metals. Related studies show that even under ideal conditions with a metallization rate of over 80%, the RHF process can achieve a potassium removal rate of 90%, but a sodium removal rate of only about 70%. Residual alkali metals entering the metallized pellets and returning to the blast furnace still pose a hazard. Furthermore, during the pyrometallurgical high-temperature reduction process, potassium and sodium compounds (such as KCl and NaCl) volatilize in large quantities above 900 °C, coexisting with the zinc and lead vapors to be recovered in the condensation system. This results in extremely high levels of potassium, sodium, and chlorine impurities in the produced zinc oxide powder. Subsequent purification of this high-impurity zinc oxide powder is difficult, leading to low product added value and severely limiting the economic viability of the process. In addition, alkali metal volatiles easily adhere to the refractory materials and linings of the equipment, causing ring formation and corrosion, thus affecting the equipment's service life.

[0006] The resource utilization of dust rich in potassium, sodium, lead, and zinc presents significant challenges. Although patents CN117070756A, CN102808087A, and CN109136575A disclose a series of methods for the resource utilization of alkali metal and lead-zinc dust, these methods generally suffer from cumbersome processes and limited processing capacity, severely restricting their large-scale application and development. Furthermore, existing pyrometallurgical treatment technologies require the introduction of additional carbon sources as reducing agents, resulting in high carbon emissions during the treatment process.

[0007] In summary, for steel metallurgical dust, existing technologies mainly focus on the metallurgical recovery and separation of heavy metals and iron, while paying less attention to the interference of alkali metals on metallurgy. In particular, for steel dust with high alkali metal content, existing technologies have not yet been able to effectively separate iron, high-content alkali metals, and heavy metals. Summary of the Invention

[0008] To address the challenges in treating steel metallurgical dust containing alkali metal M and volatile heavy metal N, this invention aims to provide a method for the selective separation of Fe, M, and N in steel metallurgical dust containing alkali metal M and volatile heavy metal N. This method aims to solve the adverse interference of high alkali metals in the dust on metallurgy and improve the selective separation effect of iron, M, and N.

[0009] For steel metallurgical dust containing volatile heavy metal nitrogen (N), the existing main approach is to reduce it to obtain elemental iron and recover the volatile N from the reduction exhaust gas. However, for steel metallurgical dust with high content of alkali metal (M) and volatile N, alkali metal (M) easily volatilizes along with N, increasing the difficulty of N recovery. Furthermore, alkali metal (M) easily caks and corrodes equipment, affecting its lifespan. To address the challenges of treating steel metallurgical powder with high content of alkali metal (M) and heavy metal (N), this invention, after in-depth research, provides the following improved solution:

[0010] A method for selectively separating Fe, M and N from iron and steel metallurgical dust containing alkali metal M and volatile heavy metal N, wherein a mixture of carbon-containing materials and iron and steel metallurgical dust is obtained, the mixture is pressed into blocks, and the blocks are heated to temperature T1 under a protective atmosphere and microwave heating, and then the atmosphere is switched to a reducing atmosphere for heat preservation and reduction treatment to obtain tail gas enriched with volatile heavy metal N and reducing slag enriched with elemental iron and alkali metal M;

[0011] The reducing slag was subjected to wet milling and leaching treatment to separate elemental iron and a solution enriched with alkali metal M.

[0012] The alkali metal M includes at least one element selected from sodium and potassium;

[0013] The volatile heavy metal N includes at least one element selected from lead and zinc;

[0014] Temperature T1 is 800~900 ℃.

[0015] Addressing the challenges of treating steelmaking dust as described in this invention, this invention utilizes a combined microwave treatment approach with carbon and reducing atmospheres, along with gas modification techniques and temperature T1 control. This synergistic effect enables efficient volatilization of metallic nitrogen (N) and controls the accompanying volatilization of metallic minerals (M), achieving highly selective volatilization of N. Furthermore, efficient separation of iron and metallic M can be achieved through simple water immersion treatment. This method avoids the accompanying volatilization of high-content metallic M and prevents the high-efficiency corrosion of reaction equipment containing metallic M.

[0016] In this invention, the contents of alkali metal M, metal N, and Fe in the mixture are not particularly required. For example, the content of alkali metal M is 4 wt% to 20 wt%; the content of volatile heavy metal N is 3 wt% to 10 wt%; and the total iron content is 20 wt% to 70 wt%. Further, the content of alkali metal M is 5 wt% to 8 wt%; the content of volatile heavy metal N is 4 wt% to 6 wt%; and the total iron content is 35 wt% to 45 wt%.

[0017] In this invention, when the carbon content in the iron and steel metallurgical powder is low, carbon elemental materials can be added; when the carbon content meets the requirements, no additional carbon material needs to be added.

[0018] In this invention, the carbon content in the mixture is fixed at 3 wt% to 15 wt%; more specifically, it can be 4 to 8 wt%.

[0019] In this invention, the pressure during the briquetting process is 3 MPa to 8 MPa. The pressurization rate can be 0.3 to 0.6 MPa / s.

[0020] In this invention, the protective atmosphere is at least one of nitrogen and an inert gas. The inert gas, for example, is a rare gas.

[0021] In this invention, the heating rate is 30~50 ℃ / min.

[0022] In this invention, the microwave power is 300~2000W during the microwave heating process.

[0023] Preferably, during microwave heating, the microwave power P1 for heating to temperature T0 is 350 W to 1300 W, more preferably 600 to 950 W; even more preferably 650 to 750 W; the microwave power P2 for heating from T0 to temperature T1 is 1.5 to 2.5 P1, preferably 1.8 to 2.2 P1; wherein T0 is 350 to 450 °C. This preferred gradient mechanism helps to further synergistically optimize the reaction behavior and further improve the selective separation of M, N, and Fe.

[0024] Studies have shown that optimized gradient power control can help further optimize reaction behavior and selectively volatilize and separate N from alkali metals M and iron.

[0025] In this invention, the reducing atmosphere is a hydrogen-containing atmosphere, wherein the hydrogen content is above 40 vol%.

[0026] Preferably, the reducing atmosphere includes H2, CO, and a buffer gas; wherein the buffer gas includes at least one of CO2 and N2; wherein the H2 concentration ranges from 40 vol% to 65 vol%, the CO concentration ranges from 25 vol% to 50 vol%, and the remainder is the buffer gas.

[0027] In this invention, the temperature T1 is 840~860 ℃; studies have shown that at this preferred temperature, combined with the overall processing technology described above, better separation selectivity of M, N and Fe can be obtained.

[0028] Preferably, the heat preservation and reduction time is 10~50 min; more preferably 20~40 min.

[0029] In this invention, the water immersion process is carried out under mechanical ball milling.

[0030] Preferably, the method for separating iron is magnetic separation.

[0031] Beneficial effects

[0032] This invention utilizes carbon-containing steel metallurgical dust as a carbonaceous reducing agent and combines it with reducing gases to make resource-based use of alkali metal and lead-zinc dust. It solves the problem that alkali metals and lead-zinc are difficult to separate through reduction, volatilization and condensation, and integrates the removal of alkali metals from dust into the grinding-magnetic separation process.

[0033] In this invention, converter dust rich in alkali metals and lead-zinc from steel plants and carbon-containing blast furnace dust were used as raw materials to verify the invention. After reduction, the iron metallization rate of the solid agglomerates reached 98.12%, the zinc volatilization rate reached 94.28%, the lead volatilization rate reached 98.62%, and the sodium and potassium volatilization rates were as low as 6.39% and 3.47%, respectively. After grinding and magnetic separation, the total iron grade of the obtained magnetic concentrate reached 95.78%, and the iron metallization rate reached 98.53%. This achieves efficient recovery of resources such as iron, lead, and zinc, and successfully overcomes the problem of difficult mixing and separation of alkali metals and lead-zinc.

[0034] Therefore, this invention has unique advantages in treating metallurgical dust containing alkali metals and lead-zinc components, and the technology has advantages such as simple process flow, low energy consumption, high production efficiency, and low carbon and environmental protection. Furthermore, the obtained direct reduced iron powder has a high grade and can be directly used as a raw material for electric arc furnace steelmaking, achieving efficient resource recovery and utilization. Attached Figure Description

[0035] Figure 1 The image shows the XRD pattern of the solid product after reduction in Example 1.

[0036] Figure 2 The XRD pattern of the reduced volatiles in Example 1;

[0037] Figure 3 The image shows the XRD pattern of the magnetic separation product from Example 1. Detailed Implementation

[0038] The present invention will be further described in detail below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] The resource utilization of dust containing potassium, sodium, iron, lead, and zinc faces a series of problems, including difficulties, high economic costs, and significant pollution emissions. This invention aims to provide a low-carbon, environmentally friendly, energy-efficient, and high-performance method for selectively dealkalizing and simultaneously recovering iron, lead, and zinc from iron and steel metallurgical dust using microwave-coupled carbon-hydrogen reduction-grinding. This invention specifically involves the following two stages.

[0040] Phase 1: Dust rich in potassium, sodium, iron, lead, and zinc is dried and mixed evenly with carbonaceous dust in a specific ratio to form briquettes. These briquettes are then heated to a designated temperature in a microwave oven under nitrogen protection. This temperature is maintained for a certain period while a reducing gas is introduced to deeply reduce the briquettes and remove lead and zinc. After the temperature is maintained, the briquettes are cooled to room temperature in a nitrogen atmosphere. During this phase, lead and zinc vapors evaporate and are recovered through condensation, while potassium, sodium, and iron remain in the solid product.

[0041] Phase Two: The cooled lumps are crushed and ball milled with a certain slurry concentration and grinding time. Then, magnetic separation is carried out to separate metallic iron from the tailings, while potassium and sodium are removed by entering the solution.

[0042] This method not only achieves the synergistic treatment of iron and steel metallurgical dust, but also realizes the gradient separation of potassium, sodium, iron, lead and zinc in the dust, providing a practical and feasible technical solution for the resource utilization of complex iron and steel metallurgical dust. The technology has a simple operation process, low pollution emissions and high efficiency, which meets the needs of future industrial technology development.

[0043] In this invention, the carbon content in the mixture is fixed at 3 wt% to 15 wt%; more specifically, it can be 4 to 8 wt%.

[0044] In this invention, the pressing process of the agglomerate needs to control the pressing rate, pressing it at a rate of 0.5 MPa / s to a pressure of 3 MPa to 8 MPa, and more preferably 4 MPa to 6 MPa.

[0045] In this invention, the reduction roasting process involves switching between different gas components, the heating process is carried out in an inert atmosphere, the reducing gas is introduced during the constant temperature roasting process to achieve deep reduction of the metal oxide, and the cooling after the reduction roasting is completed needs to be carried out in an inert atmosphere.

[0046] In this invention, the unique non-thermal effect and "hot spot" characteristics of microwaves are used to reduce and volatilize the lead-zinc components into the gas phase for condensation and recovery. The calcination temperature is not higher than 900 ℃, more preferably 780 ℃~880 ℃; and even more preferably 840~860 ℃.

[0047] In this invention, the constant temperature calcination time is generally 10 min to 50 min, and more preferably 20 min to 40 min.

[0048] In this invention, the reducing gas is composed of H2, CO, CO2 and N2, wherein the concentration of H2 ranges from 40 vol% to 65 vol%, the concentration of CO ranges from 25 vol% to 50 vol%, and CO2 and N2 are buffer gases with a total concentration range of 8 vol% to 15 vol%. More preferably, the concentrations are 50 vol% to 60 vol% for H2 and 30 vol% to 40 vol% for CO.

[0049] In this invention, the reduced solid product is subjected to a grinding-magnetic separation process to remove alkali metals and recover high-purity direct reduced iron powder. The slurry concentration is 30%~60%, the grinding time is 10 min~30 min, and the magnetic separation intensity is 400 Gs~800 Gs. More preferably, the slurry concentration is 45%~60%, the grinding time is 20 min~30 min, and the magnetic separation intensity is 500 Gs~700 Gs.

[0050] In this invention, alkali metals dissolve into an aqueous solution during the grinding-magnetic separation process to achieve separation from metallic iron.

[0051] The main chemical components of the converter dust and blast furnace dust in this invention are shown in the table below:

[0052]

[0053] —Fixed carbon.

[0054] Example 1

[0055] Step 1:

[0056] The dried carbon-containing blast furnace dust and converter dust were mixed evenly at a ratio of 1:2. The mixture was pressed into lumps at a rate of 0.5 MPa / s up to 5 MPa. The lumps were then placed in a microwave oven and preheated to temperature T0 in a protective atmosphere. After holding at T0, the temperature was further increased to T1. The atmosphere was then switched to a reducing atmosphere and reduced at temperature T1.

[0057] The microwave power for raising the initial temperature (e.g., room temperature) to 400 ℃ (marked as T0) is set to P1 (700 W), and the temperature is held for 30±5 min after raising to T0; the microwave power for raising the temperature from T0 to T1 is set to P2 (1400 W).

[0058] During the heating process, nitrogen gas was continuously introduced at a rate of 1.0 L / min for protection. When the system temperature reached 850 °C (marked as T1), the atmosphere was switched to a reducing atmosphere (H2:CO2:CO:N2 volume ratio = 55.4:34.6:3:7), and the temperature was maintained for another 30 min at a flow rate of 1.0 L / min. After the temperature maintenance was completed, the nitrogen gas was stopped and the system was cooled to room temperature in a nitrogen atmosphere. The lead and zinc volatiles and solid products were collected.

[0059] In this embodiment, the iron metallization rate of the reduced solid product was 98.12%, the zinc volatility rate was 94.28%, the lead volatility rate was 98.62%, the potassium volatility rate was 3.47%, and the sodium volatility rate was 6.39%.

[0060] Step 2:

[0061] The solid product was then crushed to less than 1.0 mm and wet ball milled. The slurry concentration was set at 50% and the grinding time was 25 min. After ball milling, magnetic separation was carried out under a magnetic field strength of 600 Gs to obtain high-purity direct reduced iron powder.

[0062] After grinding and magnetic separation, the total iron grade of the direct reduced iron powder is 95.78%, the iron metallization rate is 98.53%, and the iron recovery rate is 90.48%.

[0063] Example 2

[0064] Compared with Example 1, the only difference is that the reduction calcination temperature T1 is 900 °C, and all other operations and parameters are the same as in Example 1.

[0065] In step 1, the metallization rate of the solid product obtained by reduction was 98.91%, the zinc volatility rate was 96.86%, the lead volatility rate was 98.68%, the potassium volatility rate was 18.83%, and the sodium volatility rate was 18.62%.

[0066] In step 2, after grinding and magnetic separation, the total iron grade of the directly reduced iron powder is 94.31%, the iron metallization rate is 98.83%, and the iron recovery rate is 90.51%.

[0067] Example 3

[0068] Compared with Example 1, the only difference is that the ratio of carbon-containing blast furnace dust to converter dust in the agglomerate is 2:3, and all other operations and parameters are the same as in Example 1.

[0069] In step 1, the iron metallization rate of the solid product obtained by reduction was 96.75%, the zinc volatilization rate was 95.87%, the lead volatilization rate was 98.85%, and the potassium and sodium volatilization rates were 4.87% and 6.93%, respectively.

[0070] Example 4

[0071] Compared to Example 1, the only difference is the change in the heating mechanism; the experimental groups are as follows:

[0072] Group A: P1 and P2 are both set to P1;

[0073] Group B: P1 and P2 are both set to P2;

[0074] Group C: P1 is set to the value of P2, and the value of P2 is set to P1;

[0075] Group D: Change P1 and P2 to 900 W and 1600 W respectively.

[0076] All other operations and parameters are the same as in Example 1.

[0077] The results obtained in step 1 are as follows:

[0078] A: The iron metallization rate is 97.97%, the zinc volatility rate is 90.83%, the lead volatility rate is 96.43%, the potassium volatility rate is 3.67%, and the sodium volatility rate is 6.89%.

[0079] B: Iron metallization rate is 98.04%, zinc volatility rate is 89.21%, lead volatility rate is 85.03%, potassium volatility rate is 3.81%, and sodium volatility rate is 6.93%;

[0080] C: Iron metallization rate is 97.94%, zinc volatility rate is 90.73%, lead volatility rate is 96.51%, potassium volatility rate is 3.91%, and sodium volatility rate is 6.92%;

[0081] D: The metallization rate of iron is 98.08%, the volatility rate of zinc is 95.89%, the volatility rate of lead is 99.06%, the volatility rate of potassium is 7.35%, and the volatility rate of sodium is 9.17%.

[0082] As can be seen from Examples 1 and 4, by using the stepped two-stage microwave heating power described in this invention, the recovery of metallic N can be further enhanced, and the recovery selectivity of metallic M, N, and Fe can be improved.

[0083] Comparative Example 1

[0084] Compared with Example 1, the only difference is that in step 1, the conventional electric heating method is used instead of the microwave heating method, while the other operations and parameters are the same as in Example 1.

[0085] In step 1, the iron metallization rate of the solid product obtained by reduction was 68.73%, the zinc volatility rate was 59.62%, the lead volatility rate was 86.29%, the potassium volatility rate was 3.16%, and the sodium volatility rate was 6.61%.

[0086] In step 2, after grinding and magnetic separation, the total iron grade of the directly reduced iron powder is 86.78%, the iron metallization rate is 88.02%, and the iron recovery rate is 86.53%.

[0087] Comparative Example 2

[0088] Compared with Example 1, the only difference is that the reduction calcination temperature is 950 °C, while all other operations and parameters are the same as in Example 1.

[0089] In step 1, the potassium volatilization rate was 28.50%, and the sodium volatilization rate was 28.65%.

[0090] Comparative Example 3

[0091] Compared with Example 1, the only difference is that the reduction calcination temperature is 750 °C, while all other operations and parameters are the same as in Example 1.

[0092] In step 1, the iron metallization rate of the solid product obtained by reduction was 91.04%, the zinc volatilization rate was 54.42%, and the lead volatilization rate was 86.11%.

[0093] Comparative Example 4

[0094] The only difference from Example 1 is that the atmosphere during the heat preservation process at temperature T1 is nitrogen, and no reducing gas is introduced. All other operations and parameters are the same as in Example 1.

[0095] In step 1, the iron metallization rate of the solid product obtained by reduction was 56.07%, the zinc volatility rate was 44.97%, the lead volatility rate was 64.82%, the potassium volatility rate was 2.88%, and the sodium volatility rate was 6.42%.

[0096] Comparative Example 5

[0097] Compared with Example 1, the only difference is that carbon-containing dust is not added. For example, only converter dust is used for briquetting. All other operations and parameters are the same as in Example 1.

[0098] In step 1, the iron metallization rate of the solid product obtained by reduction was 67.31%, the zinc volatility rate was 75.98%, the lead volatility rate was 80.35%, the potassium volatility rate was 6.38%, and the sodium volatility rate was 9.08%.

[0099] Comparative Example 6

[0100] Compared with Example 1, the only difference is that the two dusts are directly mixed and then reduced without being lumped together; all other operations and parameters are the same as in Example 1.

[0101] In step 1, the iron metallization rate of the solid product obtained by reduction was 66.45%, the zinc volatility rate was 57.94%, the lead volatility rate was 60.84%, the potassium volatility rate was 4.04%, and the sodium volatility rate was 9.86%.

[0102] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be regarded as exemplary and non-limiting in all respects. The scope of the invention is defined by the appended claims rather than the foregoing description, and all changes falling within the meaning and scope of the equivalents of the claims are intended to be included within the present invention.

[0103] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style of the specification is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other implementation schemes that can be understood by those skilled in the art.

Claims

1. A method for the selective separation of Fe, M, and N in iron and steel metallurgical dust containing alkali metal M and volatile heavy metal N, characterized in that, A mixture of carbon materials and iron and steel metallurgical dust is obtained, and the mixture is pressed into blocks. The blocks are heated to temperature T1 under a protective atmosphere and microwave heating, and then the atmosphere is switched to a reducing atmosphere for heat preservation and reduction treatment to obtain tail gas enriched with volatile heavy metal N, and reducing slag enriched with elemental iron and alkali metal M. The reducing slag was subjected to wet milling and leaching treatment to separate elemental iron and a solution enriched with alkali metal M. The alkali metal M includes at least one element selected from sodium and potassium; The volatile heavy metal N includes at least one element selected from lead and zinc; Temperature T1 is 800~900 ℃.

2. The selective separation method as described in claim 1, characterized in that, The mixture contains 4 wt% to 20 wt% of alkali metal M; 3 wt% to 10 wt% of volatile heavy metal N; and 20 wt% to 70 wt% of total iron. Furthermore, the content of alkali metal M is 5 wt%~8 wt%; the content of volatile heavy metal N is 4 wt%~6 wt%; and the total iron content is 35 wt%~45 wt%.

3. The selective separation method as described in claim 1, characterized in that, The carbon content in the mixture is fixed at 3 wt% to 15 wt%; it can be further set at 4 to 8 wt%.

4. The selective separation method as described in claim 1, characterized in that, The pressure during the briquetting process is 3 MPa to 8 MPa.

5. The selective separation method as described in claim 1, characterized in that, The protective atmosphere is at least one of nitrogen and an inert gas.

6. The selective separation method as described in claim 1, characterized in that, The heating rate is 30~50 ℃ / min.

7. The selective separation method as described in claim 1, characterized in that, During microwave heating, the microwave power is 300~2000W; Preferably, during the microwave heating process, the microwave power P1 for heating to temperature T0 is 350 W to 1300 W; the microwave power P2 for heating from T0 to temperature T1 is 1.5 to 2.5P1; wherein T0 is 350 to 450 °C.

8. The selective separation method as described in claim 1, characterized in that, The reducing atmosphere is a hydrogen-containing atmosphere, wherein the hydrogen content is above 40 vol%. Preferably, the reducing atmosphere includes H2, CO, and a buffer gas; wherein the buffer gas includes at least one of CO2 and N2; wherein the H2 concentration ranges from 40 vol% to 65 vol%, the CO concentration ranges from 25 vol% to 50 vol%, and the remainder is the buffer gas.

9. The selective separation method as described in claim 1, characterized in that, Temperature T1 is 840~860 ℃; Preferably, the heat preservation and reduction time is 10~50 min; more preferably 20~40 min.

10. The selective separation method as described in claim 1, characterized in that, The water immersion process is carried out under mechanical ball milling. Preferably, the method for separating iron is magnetic separation.

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